1. Field of the Invention
The present invention generally relates to a recording clock generating apparatus for a data recording system. In particular, the present invention relates to a recording clock generating apparatus which produces a recording clock signal for a data recording system in which a write head records data onto an optical disk or another recording medium by sending a powered pulse of a laser beam at a rate that is synchronized with the recording clock signal produced by the recording clock generating apparatus.
2. Description of the Related Art
CD-ROMs (compact disk read-only-memories) and DVDs (digital versatile disks) are read-only, optical recording media, and have their rewritable equivalents, respectively. CD-ROM has a rewritable equivalent in CD-R (compact disk recordable). DVD has DVD-R (digital versatile disk recordable). Similar to a hard disk or the like, data can be recorded onto the rewritable media. CD-R and DVD-R differ in how much data can be written to them.
Both CD-R and DVD-R include a disk surface portion in which wobble grooves are formed in order to create a wobble signal indicative of rotation control sync information from the wobble grooves. In the disk surface portion of CD-R and DVD-R, the wobble grooves extend in a tangential track direction of the disk, and prepits are formed as the preformat information on the lands between neighboring grooves.
As the information recording capacity of DVD-R is much higher than the capacity of CD-R, a track pitch of DVD-R, which is a center-to-center distance between the neighboring grooves in the radial direction, is smaller than a track pitch of CD-R. In the case of DVD-R, because of the smaller track pitch, the crosstalk of neighboring grooves will not be negligible.
In certain circumstances when recording data onto a DVD-R, the sampled wobble signal, which is obtained from the DVD-R, may have significant variances of the amplitude and the phase due to the crosstalk of neighboring grooves. In this case, it is difficult to produce a recording clock signal that is precisely synchronized with the rotation of the disk, if the recording clock signal is produced based on the sampled wobble signal.
Japanese Laid-Open Patent Application No. 10-293926 discloses a recording clock generating device, which produces a recording clock signal synchronized with rotation of an optical disk. The recording clock generating device of the above publication is configured to eliminate the above-described problem.
In the above recording clock generating device, a prepit detector receives a composite signal superimposed with a prepit signal, and outputs a prepit detection signal during the presence of the prepit signal. A wobble signal sampler outputs an amplitude level of the composite signal when a sampled wobble signal continues to be at a high level over a period exceeding a predetermined reference time.
In the above recording clock generating device, a PLL (phase-locked loop) circuit outputs a clock signal, which is phase-locked to the sampled wobble signal, to a phase shifter. On the other hand, a phase comparator compares the phase of the prepit detection signal with the phase of the sampled wobble signal, and outputs a phase adjustment signal to the phase shifter. Then, the phase shifter adjusts the phase of the clock signal based on the phase adjustment signal, and the clock signal with the thus adjusted phase is delivered to the write head control module of the data recording system.
However, the above recording clock generating device requires the phase shifter that adjusts the phase of the clock signal based on the phase adjustment signal. There was a problem in that the phase shifter is expensive and the use of the phase shifter considerably raises the manufacturing cost of the recording clock generating device.